The invention relates to a three layer of multi-layer paper machine wire in form of a composite fabric for the wet end of a paper making machine, comprising a three layer or multi-layer paper machine wire in form of a compound fabric for the wet end of the paper machine, comprising at least on upper fabrics on the paper side, at least one lower fabric on the running side and binding threads directed cross to the running direction of the wire, by which the upper fabric and the lower fabric have been connected by weaving.
Known paper machine wires of such a kind have the object to dewater the fiber suspension and to form thereby a stabilized wet paper web which can be carried on the paper machine wire to the press section of the paper machine. For that purpose the paper machine wire has the form of an endless belt circulating within the roll system or dewatering system, respectively of the wet end of the paper machine with high speed.
From practice paper machine wires of the above mentioned kind are known. These wires, which are also called paper machine forming fabrics, comprise on their paper side a very fine fabric, in the following called upper fabric, preferably woven in plain weave, and on their running side directed to the paper machine a wearing fabric, in the following called lower fabric, and corresponding with respect to its warp thread number and weft thread number preferably those of the upper fabric. The lower fabric is generally manufactured with a satin binding or twill binding. The upper and the lower fabrics are connected by binding threads extending for instance cross to the running direction of the wire. Under operation of such paper machine wires on especially modem paper machines operating with high speed often waves are formed in the fabric causing essential reductions of the quality of the manufactured paper.
Therefore, the main object underlying the present invention is to provide the paper machine wire of the above mentioned kind the stability of which in cross direction is improved.
It is a further object of the invention to improve the dewatering characteristics of the fabric and in this connection its permeability.
According to still a further object of the invention the paper machine wire is to be provided with a greater volume.
These and other objects are solved according to the present invention by providing a paper machine wire comprising an additional group of weft threads provided between the weft thread layer of the at least one upper fabric and the weft thread layer of the at least one lower fabric.
Because of the above mentioned features the paper machine wire gets an increased bending strength in cross-direction, ie. cross to its running direction. Thus, the paper machine wire comprises a greater volume having an advantageous effect on the formation of the paper dependant on the construction of the forming section of the paper machine. A greater volume may also result, however, in an improvemed permeability of the fabric so that dewatering of the fiber suspension will be more rapidly by using such a wire.
According to an advantageous embodiment of the subject invention the weft thread layer of the at least one upper fabric and the weft thread layer of the at least one lower fabric are separated from one another by additional weft thread groups. Thus, the upper layer is lifted from the lower layer so that an additional increase of the volume of the paper machine wire and of the stiffness or stability of the wire is caused.
According to a further advantageous embodiment of the subject invention the threads of the additional weft thread group and the binding threads woven between the at least one upper fabric and the at least one lower fabric change with respect to one another. Because of this the additional weft thread group causes an approved protection of the interwoven binding threads in cross-direction, as the upper fabric and the lower fabric are no longer exclusively separated by the binding threads which are binding through but also by the additional weft thread group. Moreover, the positioning stability of the binding threads in longitudinal direction or binding direction of the wire is improved thereby.
According to a further embodiment of the invention all weft threads of the upper fabric run over the threads of the additional group of weft threads and all warp threads of the lower fabric run below the threads of the additional group of weft threads. For that reason a clear separation of the layers is gained, i.e. a clear separation of the upper fabric and the lower fabric, so that the threads of the upper fabric do not directly bind into the lower fabric and the threads of the lower fabric do not directly bind into the upper fabric.
Moreover, it is advantageous to put the threads of the welt layer of the at least one upper fabric, the threads of the weft layer of at least the one lower fabric and the threads of the additional group of weft threads in one and the same approximately vertical level in order to gain a clear separation between the threads of the weft layer of the upper fabric and those of the weft layer of the lower fabric.
According to a further advantageous embodiment of the subject invention the threads of the additional group of weft threads are in vertical direction displaced with respect to the threads of the weft layer of the at least one upper fabric and the threads of the weft layer of the at least one lower fabric. By such an arrangement of the additional group of weft threads not only the bending strength of the wire is increased but also in addition to that the permeability of the wire is reduced. Thus, these properties of the wire may be precisely set by the arrangement of the additional weft thread group according to the invention.